3 Health as a test of skill
TBoI uses health as a test of skill in a very interesting way.
Starting from floor 2 (Basement 2) and until floor 8 (Womb 2) you start each floor with a nonzero chance of getting a Devil Room after defeating the floor’s Boss.7 This chance is relatively high (from 33.75% up to 100%) until you get damaged. Then it’s drastically reduced down to a 0.25% to 9% chance.
OK, it’s more complicated than that.
Your chances for getting a Devil Room are only reduced if you receive red heart damage. What this means is that the first purpose of Soul/Demon hearts is now evident: they effectively serve as a shield for your red hearts so that you can get to the Devil Room safely. No extra hearts means you need te be extra careful to not take any damage in during the whole floor.
If this sounds daunting is because it’s designed that way. This is similar to many other games, most notably the Dark Souls series: the game rewards knowing your enemies and their attack patterns, having good situational awareness and prioritizing some enemies above others.
Also, as the game progresses, the game’s difficulty goes up. In order to maintain your odds of getting a Devil Room you need to step up not only your own abilities as a player, but also your character’s general prowess (speed, damage, fire rate, etc.) This too requires knowledge of the game and its items: some items are just not worth it and some are useful only in very specific circumstances8.
2: Other sources of health
← Health in The Binding of Isaac
→ 4: Health as a Risk/Reward mechanism
Technically, you can get to the Devil Room in all floors with a lucky Red Chest or via the use of the Joker card, but those have nothing to do with the actual Health management that is the focus of this guide↩︎
For instance the item Soy Milk. It’s a terrible item to have because it drastically lowers your damage while turning your fire rate up to eleven. But if you manage to have both Soy Milk and Libra (which “balances” all your stats) you end up with a decent fire rate and damage, good enough for almost all floors.↩︎